maven-jar-plugin 指定mainClass

Question

I am trying to run a Java10 "hello world" example from the commandline that I have created using maven.

But I get the message

Error: Could not find or load main class App in module eu.ngong.mainclass

It works with

mvn exec:java -Dexec.mainClass=eu.ngong.mainclass.App

but not if I run the script

p=~/.m2/repository/eu/ngong/mainclass/1.0.0
java -p $p -m eu.ngong.mainclass.App

The pom.xml is:

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>

<groupId>eu.ngong</groupId>
<artifactId>mainclass</artifactId>
<version>1.0.0</version>
<packaging>jar</packaging>

<name>mainclass</name>
<url>http://maven.apache.org</url>

<properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>

<build>
    <pluginManagement>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.8.0</version>
                <configuration>
                    <release>10</release>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-jar-plugin</artifactId>
                <version>3.1.0</version>
                <configuration>
                    <archive>
                        <manifest>
                            <mainClass>eu.ngong.mainclass.App</mainClass>
                        </manifest>
                    </archive>
                </configuration>
            </plugin>
        </plugins>
    </pluginManagement>
</build>

<dependencies>
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.12</version>
    </dependency>
</dependencies>

If I look into the jar, I can find the App class, as well as the MANIFEST.MF

Manifest-Version: 1.0
Created-By: Apache Maven 3.5.4
Built-By: rsc
Build-Jdk: 10.0.2
Main-Class: eu.ngong.mainclass.App

What did I miss?

I pushed the project here

Answer 1

Try updaing the pom with <addClasspath>true</addClasspath> as well in maven-jar-plugin as below under configuration . It cannot correctly find the main class when the class path is not set.

 <archive>
        <manifest>
          <addClasspath>true</addClasspath>
          <mainClass>eu.ngong.mainclass.App</mainClass>
        </manifest>
      </archive>

Answer 2

mvn clean deletes all compiled classes.

mvn exec:java runs the only the goal java of the plugin exec . But it is missing the compiled classes, that you clean ed before.

mvn test asks maven to run all lifecycles up to the test phase - including the compile lifecycle.

mvn compile exec:java would run everything including the compile phase (which should be enough for exec:java goal) and then the exec:java goal. You can separated it also in two calls.